An electrode interface, that has high selectivity and is reliable, at proximal peripheral nerve stumps is desirable for amputees and patients with peripheral nerve injury. For example, the peripheral signal recorded from the amputees and patients can be used to control an artificial limb. Alternatively, the ability to record a neural signal from the proximal nerve stump and to actuate target muscle fibres via a wireless link shows an opportunity to bypass reliance on the natural ability of the nerve to regenerate and to restore limb movement of patients with peripheral nerve injury.
Regenerative electrodes show potential for high selectivity and reliable peripheral nerve interfaces (PNI). An example is a sieve electrode which can be fabricated from silicon (Si), polymer and epoxy. The sieve electrode is placed between two cut ends of a nerve trunk and some of the sieve electrode holes are constructed with ring electrodes. After the nerve fibres regenerate through the holes, an intimate electrical contact can be formed, thus allowing both reliable recording of neural signals and efficient stimulation on the residual nerve fibers.
However, applicability of sieve electrodes is critically dependent on the success of axonal regeneration through the holes with an electrode and the time taken for axonal regeneration. For amputees (who suffer loss of the distal nerve stump) or when separation between the proximal nerve stump and the distal nerve stump in a patient is too far way for axonal regeneration, the proximal nerve stump needs to be surgically reinnervated into other spare muscles. This could result in painful neuromas. For such circumstances, polyimide based sieve-like electrodes have been proposed. The device has a fixation flap structure and integrated biological cells. The device may be adapted for use with a distal nerve stump without a guidance tube, but it cannot be adapted for use with a proximal nerve stump.
Various other methods, including chemical and topographic methods, have been proposed to guide and promote axonal regeneration. For instance, a regenerative electrode design has been proposed containing multiple microfluidic channels that serve as a guidance tube for nerve regeneration and as fluidic pathways for injecting chemicals such as nerve growth factors (NGF) to promote nerve growth. Alternatively, an electrode design with micro-channels structure having embedded biodegradable polymer has been proposed. The drugs for promoting and guiding nerve regeneration are incorporated into the polymer and released into the body during the polymer degradation. However, both of these designs introduce additional massive micro-channel structures, which can trigger an extra tissue response when compared to the standard sieve electrode. Further, delivering drugs through microfluidic channels requires an external pump system and the dosage of drugs is constrained in the biodegradable polymer approach.
Research has gone into creating various topographic structures to direct regenerating axons though electrode holes, but the topographic structures introduce an additional massive-structure into the standard sieve electrode. Finally, research effort has been put into the modification of guidance tubes (or conduits) to promote and guide nerve regeneration. However, these approaches can only guide the nerve growth through the guidance tube rather than guide the nerve growth through the sieve holes with an electrode.
There is thus a need to address the above drawbacks relating to interfaces that promote axonal regeneration.